02-26-2016 08:41 PM - edited 02-26-2016 08:44 PM
There is no function for 'zip to county code', and I think the reason lies in the fact that it is not uncommon one zipcode could be shared by multiple counties(Some say as many as 20%).
@Reeza is correct, you need to use sashelp.zipcode table, with the help of city name you have, your zip code should reach a satisfactory pin down on county code.
When using sashelp.zipcode, the 'county' variable is the county code within states. If you need five digits county code, you need to concatenate 'state' as z2. and 'county' as z3.